The Pd(II)-acetate catalyzed ring closure of halogenated diphenyl ethers and benzophenones is being utilized to synthesize halogenated dibenzofurans and fluorenones. A polybrominating agent, dibromoisocyanuric acid, is used to obtain certain polybrominated naphthalenes and biphenylenes. Such polyhalogenated aromatic compounds are of current toxicological interest as potential persistent environmental agents.